1. Field of the Invention
The present invention relates to a gas separation membrane and a gas separation membrane module. More specifically, the present invention relates to a gas separation membrane which has high gas permeability and high gas separation selectivity and a gas separation membrane module which has the gas separation membrane.
2. Description of the Related Art
A material formed of a polymer compound has a gas permeability specific to the material. Based on this property, it is possible to cause selective permeation and separation out of a target gas component using a membrane formed of a specific polymer compound (gas separation membrane). As an industrial use aspect for this gas separation membrane related to the problem of global warming, separation and recovery from large-scale carbon dioxide sources with this gas separation membrane has been examined in thermal power plants, cement plants, or ironworks blast furnaces. Further, this membrane separation technique has been attracting attention as a means for solving environmental issues which can be achieved with relatively little energy. In addition, the technique is being examined as a means for removing carbon dioxide from natural gas or biogas (biological excrement, organic fertilizers, biodegradable substances, sewage, garbage, fermented energy crops, or gas generated due to anaerobic digestion).
As a membrane separation method for securing gas permeability and gas separation selectivity by making a site contributing to gas separation into a thin layer to be used as a practical gas separation membrane, a method of making a portion contributing to separation serving as an asymmetric membrane into a thin layer which is referred to as a skin layer, a method of using, as materials having mechanical strength, a support and a thin film composite provided with a selective layer contributing to gas separation which is disposed on the support, or a method of using hollow fibers including a layer which contributes to gas separation and has high density is known. In the above-described methods, layers contributing to gas separation are commonly referred to as separation layers.
In a gas separation membrane, gas separation selectivity is expressed by means of using a material with high gas separation selectivity as a separation layer contributing to separation. The gas purity can be increased by unn gas in mixed gas selectively passing through a membrane.
An example in which a separation membrane is formed using a block copolymer such as a diblock copolymer having a binary system or a triblock terpolymer having a ternary system as a material of the separation membrane is known.
For example, JP2008-189910A describes a method of obtaining a microporous membrane suitable to be used as a separation membrane such as a microfiltration membrane or an ultrafiltration membrane by means of using a polymer consisting of three kinds of segments. The paragraph [0044] describes a form in which pores are formed such that both main surfaces of the membrane are connected to each other. Further, a pore structure having such through-holes is also known in fields other than separation membranes, and JP2005-97625A describes a method of preparing a hierarchical structure, which has through-holes, using a block copolymer.
Moreover, as literature suggesting that a block copolymer is used as a gas separation membrane, Journal of the Adhesion Society of Japan 33 (2), Furukawa et. al., pp. 63 to 73, 1997-02-01; Journal of Membrane Science 206 (2002), pp. 149 to 163; and Journal of Membrane Science 323 (2008), pp. 53 to 59, can be exemplified.
Journal of the Adhesion Society of Japan 33 (2), Furukawa et. al., pp. 63 to 73, 1997-02-01 suggests that a statistical copolymer of polyimide containing siloxane which has a structure having a segment formed of repeating units of dimethylsiloxane and an imide and a segment of polyimide in the main chain has a microphase-separated structure, but there is no description of the relationship between the phase-separated structure and the film thickness.
Journal of Membrane Science 206 (2002), pp. 149 to 163 discloses a statistical copolymer of polyimide containing siloxane which has a structure having a segment formed of repeating units of dimethylsiloxane and an imide and a segment formed of repeating units of diphenyl ether and an imide in the main chain and also discloses data related to gas separation selectivity, but the internal structure of a polymer layer or the film thickness has not been researched.
Journal of Membrane Science 323 (2008), pp. 53 to 59 discloses a statistical copolymer of polyimide which has a structure having a segment formed of repeating units of diphenyl ether and an imide and a segment formed of repeating units of diamine-containing polyethylene glycol and an imide and also discloses data related to gas separation selectivity, but the internal structure of a polymer layer or the film thickness has not been researched.
Here, in a case where the thickness of the separation layer is uniform, the selectivity for gases is not greatly affected by the thickness thereof, but the permeability is greatly affected by that. When the thickness thereof is uniform, the gas permeability may increase as the separation layer becomes thinner and the processing capacity of mixed gas can be increased when the gas separation selectivity does not deteriorate. However, when the separation layer is practically intended to be thinned, the probability that defects (for example, through-holes passing through the separation layer) will be generated in a part of the membrane becomes higher. For this reason, practically, there is a lower limit when thinning the separation layer while the gas separation selectivity is maintained.
An object of the present invention is to provide a gas separation membrane which has high gas permeability and high gas separation selectivity.